It is desirable to utilize multiple pumps in a single borehole for number of reasons. First, multiple pumps may be used to increase the output from a well by combining the outputs of more than one pump. When only single phase power is available, combining multiple pumps to meet requirements is highly desirable. Second, multiple pumps may be utilized to efficiently accommodate a varying output requirement, such as by utilizing one pump for base load requirements and operating a second or subsequent pump only when additional output is desired. Third, some users find that is desirable to utilize one pump as a primary pump, and to maintain a second pump as a backup.
The primary restriction on pump selection for a well is the diameter of the well. Since it is necessary to lower the pump assembly into the well, the well bore must be of sufficient diameter to accommodate the selected pump or pumps. In as much as the cost of drilling a well increases substantially with the diameter of the well, it is desirable to maximize the output obtained from a well by maximizing the pumping capacity placed downhole. Rather than selecting the expensive alternative of increasing the bore diameter of a well in order to accommodate multiple pumps in a side-by-side fashion, one solution which has heretofore been proposed is to supplement a first well pump with a second well pump positioned below it in the well bore.
One problem which must be overcome with such a solution is that the discharge line from the first pump must be accommodated with respect to the placement of the second pump. In other words, the use of a second pump necessitates adapting the cross-sectional shape of the discharge pipe from the lower pump to accommodates the shape of the pump thereabove. This problem is further aggravated by the fact that the lower pump is supported by its discharge pipe within the well bore. Thus, the discharge pipe is continuously subjected to various stresses. The weight of the lower pump is by its discharge pipe. When the pump operates, any vibration, including those generated when stopping and starting, are transmitted to the discharge pipe. Also, repeated pressurization by the pump of the discharge pipe, and depressurization upon cessation of operation, subjects the discharge pipe to stress cycling.
Unfortunately, in the prior art designs for such multiple pump tools which are known to me, over extended periods of time the varying mechanical stresses and strains on the discharge pipe combined with the internal fluid pressure cycling has resulted in deformation and occasional rupturing of such parts. Further, many of the heretofore available designs known to me are likely to deform to an extent that makes retrieval from the well difficult, if not impossible. Also, many of the pump tool designs heretofore proposed do not provide what I consider to be an adequate system for structural reinforcement to insure long life downhole and retrievability of the tool as desired., Therefore, a continuing demand exists for a simple, inexpensive and reliable multiple pump tool assembly. More particularly, there exists a demand for a multiple pump tool assembly which provides a good structural design to assure long service life.
Several multiple pump tool assemblies of the character described above which provide to some limited extent the general capabilities desired have heretofore been proposed. Those of which I am aware are disclosed in U.S. Pat. Nos.: 4,548,263 issued Oct. 22, 1985 to B. E. Woods for FITTING FOR DUAL SUBMERSIBLE PUMPS; and 3,741,298 issued June 26, 1973 to Lawrence J. Canton for MULTIPLE WELL PUMP ASSEMBLY.
For the most part, the documents identified in the preceding paragraph disclose devices which have one or more of the following shortcomings: (a) they lack sufficient structural design to minimize deformation, and as a result, (b) their design fails to assure long service life or retrievability of the tool and appended pumps.
Therefore, there still remains an unmet and increasingly important need in the field for a vertically disposed multiple pump assembly which is designed and manufactured in a way that assures sufficient structural strength to withstand years of use and which have the assurance that retrieval from downhole is possible whenever required. Thus, the advantages of the reinforced and structurally sound design of my multiple well pump tool assembly are important and self-evident.